This invention relates to a low temperature process suitable for forming stress-reduced thin films which are ballistically alloyed onto a substrate in a high vacuum, hydrogen-free atmosphere, the coated article formed by the process and the accompanying apparatus. More particularly, the invention relates to a method which simultaneously utilizes a low energy sputtered beam and a high energy bombarding beam to produce thin, pure, stress-reduced hard films such as polycrystalline diamond which can be bonded to a wide variety of substrates; the deposited coatings being bonded to the substrate within a thin, boundary zone in which the deposited layer has physically mixed and/or chemically bonded onto the substrate.